Apparently there is some argument over this. The most commonly cited website says they were introduced in 1940. However, I found a discussion over at the Axis History Forum linkthat has the following citation:

"You should look at the reliable authors Doyle and Jentz. In Panzer Tracts No.15-2 they state "that ONE Entwicklungsstueck (development piece) was delivered in May 1941. Mass production had delivered 80 by July/August 1941"."

Doyle and Jentz seem to be pretty good on this sort of thing, so I would probably go with that. Others will probably be along to dispute this, but it does seem that your force might have some.BWW

Good question, think it's come up before on TMP and someone may have found a definitive answer. The first time they appear on the authorised organisation tables is Nov 1941, which should cover your winter 1941 onwards timeframe.